Digital imaging systems (e.g., cameras) have quickly become a standard feature for portable devices including portable multimedia players, smart phones, and tablet computers. The image quality expected from these portable cameras has grown as higher quality and higher megapixel cameras have been incorporated into such small devices. As portable device dimensions shrink, so do the dimensions of the incorporated camera modules. At such small scales, mass produced camera modules become more susceptible to image quality degradation due to slight deviations or variations in the optical components introduced during manufacture or imaging system assembly. Sharpness degradation is an example of such detrimental degradation that could arise in such cases.
Several quality analysis metrics may be used to describe different aspects of image quality in a captured, digital image, to identify detrimental degradations during manufacturing test. For one, test systems may measure the sharpness of an image produced by an imaging system. The sharpness may vary in different parts of the captured image, where typically the center of the digital image may be sharper than its corner. Still further, test systems may monitor spatial sharpness in different directions (e.g., meridional, sagittal, horizontal, vertical). Such tests use the concept of a slanted edge based spatial frequency response (SFR) where an SFR curve is computed for edges captured in a digital image. Computation costs for SFR-based testing increases for increased image field coverage, which makes full field SFR tests impractical for fast, mass production quality testing.